(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
      // AMD. Register as an anonymous module unless amdModuleId is set
      define([], function () {
        return (root['SignaturePad'] = factory());
      });
    } else if (typeof exports === 'object') {
      // Node. Does not work with strict CommonJS, but
      // only CommonJS-like environments that support module.exports,
      // like Node.
      module.exports = factory();
    } else {
      root['SignaturePad'] = factory();
    }
  }(this, function () {
  
  /*!
   * Signature Pad v1.5.3
   * https://github.com/szimek/signature_pad
   *
   * Copyright 2016 Szymon Nowak
   * Released under the MIT license
   *
   * The main idea and some parts of the code (e.g. drawing variable width Bézier curve) are taken from:
   * http://corner.squareup.com/2012/07/smoother-signatures.html
   *
   * Implementation of interpolation using cubic Bézier curves is taken from:
   * http://benknowscode.wordpress.com/2012/09/14/path-interpolation-using-cubic-bezier-and-control-point-estimation-in-javascript
   *
   * Algorithm for approximated length of a Bézier curve is taken from:
   * http://www.lemoda.net/maths/bezier-length/index.html
   *
   */
  var SignaturePad = (function (document) {
      "use strict";
  
      var SignaturePad = function (canvas, options) {
          var self = this,
              opts = options || {};
  
          this.velocityFilterWeight = opts.velocityFilterWeight || 0.7;
          this.minWidth = opts.minWidth || 0.5;
          this.maxWidth = opts.maxWidth || 2.5;
          this.dotSize = opts.dotSize || function () {
              return (this.minWidth + this.maxWidth) / 2;
          };
          this.penColor = opts.penColor || "black";
          this.backgroundColor = opts.backgroundColor || "rgba(0,0,0,0)";
          this.onEnd = opts.onEnd;
          this.onBegin = opts.onBegin;
  
          this._canvas = canvas;
          this._ctx = canvas.getContext("2d");
          this.clear();
  
          // we need add these inline so they are available to unbind while still having
          //  access to 'self' we could use _.bind but it's not worth adding a dependency
          this._handleMouseDown = function (event) {
              if (event.which === 1) {
                  self._mouseButtonDown = true;
                  self._strokeBegin(event);
              }
          };
  
          this._handleMouseMove = function (event) {
              if (self._mouseButtonDown) {
                  self._strokeUpdate(event);
              }
          };
  
          this._handleMouseUp = function (event) {
              if (event.which === 1 && self._mouseButtonDown) {
                  self._mouseButtonDown = false;
                  self._strokeEnd(event);
              }
          };
  
          this._handleTouchStart = function (event) {
              if (event.targetTouches.length == 1) {
                  var touch = event.changedTouches[0];
                  self._strokeBegin(touch);
               }
          };
  
          this._handleTouchMove = function (event) {
              // Prevent scrolling.
              event.preventDefault();
  
              var touch = event.targetTouches[0];
              self._strokeUpdate(touch);
          };
  
          this._handleTouchEnd = function (event) {
              var wasCanvasTouched = event.target === self._canvas;
              if (wasCanvasTouched) {
                  event.preventDefault();
                  self._strokeEnd(event);
              }
          };
  
          this._handleMouseEvents();
          this._handleTouchEvents();
      };
  
      SignaturePad.prototype.clear = function () {
          var ctx = this._ctx,
              canvas = this._canvas;
  
          ctx.fillStyle = this.backgroundColor;
          ctx.clearRect(0, 0, canvas.width, canvas.height);
          ctx.fillRect(0, 0, canvas.width, canvas.height);
          this._reset();
      };
  
      SignaturePad.prototype.toDataURL = function (imageType, quality) {
          var canvas = this._canvas;
          return canvas.toDataURL.apply(canvas, arguments);
      };
  
      SignaturePad.prototype.fromDataURL = function (dataUrl) {
          var self = this,
              image = new Image(),
              ratio = window.devicePixelRatio || 1,
              width = this._canvas.width / ratio,
              height = this._canvas.height / ratio;
  
          this._reset();
          image.src = dataUrl;
          image.onload = function () {
              self._ctx.drawImage(image, 0, 0, width, height);
          };
          this._isEmpty = false;
      };
  
      SignaturePad.prototype._strokeUpdate = function (event) {
          var point = this._createPoint(event);
          this._addPoint(point);
      };
  
      SignaturePad.prototype._strokeBegin = function (event) {
          this._reset();
          this._strokeUpdate(event);
          if (typeof this.onBegin === 'function') {
              this.onBegin(event);
          }
      };
  
      SignaturePad.prototype._strokeDraw = function (point) {
          var ctx = this._ctx,
              dotSize = typeof(this.dotSize) === 'function' ? this.dotSize() : this.dotSize;
  
          ctx.beginPath();
          this._drawPoint(point.x, point.y, dotSize);
          ctx.closePath();
          ctx.fill();
      };
  
      SignaturePad.prototype._strokeEnd = function (event) {
          var canDrawCurve = this.points.length > 2,
              point = this.points[0];
  
          if (!canDrawCurve && point) {
              this._strokeDraw(point);
          }
          if (typeof this.onEnd === 'function') {
              this.onEnd(event);
          }
      };
  
      SignaturePad.prototype._handleMouseEvents = function () {
          this._mouseButtonDown = false;
  
          this._canvas.addEventListener("mousedown", this._handleMouseDown);
          this._canvas.addEventListener("mousemove", this._handleMouseMove);
          document.addEventListener("mouseup", this._handleMouseUp);
      };
  
      SignaturePad.prototype._handleTouchEvents = function () {
          // Pass touch events to canvas element on mobile IE11 and Edge.
          this._canvas.style.msTouchAction = 'none';
          this._canvas.style.touchAction = 'none';
  
          this._canvas.addEventListener("touchstart", this._handleTouchStart);
          this._canvas.addEventListener("touchmove", this._handleTouchMove);
          this._canvas.addEventListener("touchend", this._handleTouchEnd);
      };
  
      SignaturePad.prototype.on = function () {
          this._handleMouseEvents();
          this._handleTouchEvents();
      };
  
      SignaturePad.prototype.off = function () {
          this._canvas.removeEventListener("mousedown", this._handleMouseDown);
          this._canvas.removeEventListener("mousemove", this._handleMouseMove);
          document.removeEventListener("mouseup", this._handleMouseUp);
  
          this._canvas.removeEventListener("touchstart", this._handleTouchStart);
          this._canvas.removeEventListener("touchmove", this._handleTouchMove);
          this._canvas.removeEventListener("touchend", this._handleTouchEnd);
      };
  
      SignaturePad.prototype.isEmpty = function () {
          return this._isEmpty;
      };
  
      SignaturePad.prototype._reset = function () {
          this.points = [];
          this._lastVelocity = 0;
          this._lastWidth = (this.minWidth + this.maxWidth) / 2;
          this._isEmpty = true;
          this._ctx.fillStyle = this.penColor;
      };
  
      SignaturePad.prototype._createPoint = function (event) {
          var rect = this._canvas.getBoundingClientRect();
          return new Point(
              event.clientX - rect.left,
              event.clientY - rect.top
          );
      };
  
      SignaturePad.prototype._addPoint = function (point) {
          var points = this.points,
              c2, c3,
              curve, tmp;
  
          points.push(point);
  
          if (points.length > 2) {
              // To reduce the initial lag make it work with 3 points
              // by copying the first point to the beginning.
              if (points.length === 3) points.unshift(points[0]);
  
              tmp = this._calculateCurveControlPoints(points[0], points[1], points[2]);
              c2 = tmp.c2;
              tmp = this._calculateCurveControlPoints(points[1], points[2], points[3]);
              c3 = tmp.c1;
              curve = new Bezier(points[1], c2, c3, points[2]);
              this._addCurve(curve);
  
              // Remove the first element from the list,
              // so that we always have no more than 4 points in points array.
              points.shift();
          }
      };
  
      SignaturePad.prototype._calculateCurveControlPoints = function (s1, s2, s3) {
          var dx1 = s1.x - s2.x, dy1 = s1.y - s2.y,
              dx2 = s2.x - s3.x, dy2 = s2.y - s3.y,
  
              m1 = {x: (s1.x + s2.x) / 2.0, y: (s1.y + s2.y) / 2.0},
              m2 = {x: (s2.x + s3.x) / 2.0, y: (s2.y + s3.y) / 2.0},
  
              l1 = Math.sqrt(dx1*dx1 + dy1*dy1),
              l2 = Math.sqrt(dx2*dx2 + dy2*dy2),
  
              dxm = (m1.x - m2.x),
              dym = (m1.y - m2.y),
  
              k = l2 / (l1 + l2),
              cm = {x: m2.x + dxm*k, y: m2.y + dym*k},
  
              tx = s2.x - cm.x,
              ty = s2.y - cm.y;
  
          return {
              c1: new Point(m1.x + tx, m1.y + ty),
              c2: new Point(m2.x + tx, m2.y + ty)
          };
      };
  
      SignaturePad.prototype._addCurve = function (curve) {
          var startPoint = curve.startPoint,
              endPoint = curve.endPoint,
              velocity, newWidth;
  
          velocity = endPoint.velocityFrom(startPoint);
          velocity = this.velocityFilterWeight * velocity
              + (1 - this.velocityFilterWeight) * this._lastVelocity;
  
          newWidth = this._strokeWidth(velocity);
          this._drawCurve(curve, this._lastWidth, newWidth);
  
          this._lastVelocity = velocity;
          this._lastWidth = newWidth;
      };
  
      SignaturePad.prototype._drawPoint = function (x, y, size) {
          var ctx = this._ctx;
  
          ctx.moveTo(x, y);
          ctx.arc(x, y, size, 0, 2 * Math.PI, false);
          this._isEmpty = false;
      };
  
      SignaturePad.prototype._drawCurve = function (curve, startWidth, endWidth) {
          var ctx = this._ctx,
              widthDelta = endWidth - startWidth,
              drawSteps, width, i, t, tt, ttt, u, uu, uuu, x, y;
  
          drawSteps = Math.floor(curve.length());
          ctx.beginPath();
          for (i = 0; i < drawSteps; i++) {
              // Calculate the Bezier (x, y) coordinate for this step.
              t = i / drawSteps;
              tt = t * t;
              ttt = tt * t;
              u = 1 - t;
              uu = u * u;
              uuu = uu * u;
  
              x = uuu * curve.startPoint.x;
              x += 3 * uu * t * curve.control1.x;
              x += 3 * u * tt * curve.control2.x;
              x += ttt * curve.endPoint.x;
  
              y = uuu * curve.startPoint.y;
              y += 3 * uu * t * curve.control1.y;
              y += 3 * u * tt * curve.control2.y;
              y += ttt * curve.endPoint.y;
  
              width = startWidth + ttt * widthDelta;
              this._drawPoint(x, y, width);
          }
          ctx.closePath();
          ctx.fill();
      };
  
      SignaturePad.prototype._strokeWidth = function (velocity) {
          return Math.max(this.maxWidth / (velocity + 1), this.minWidth);
      };
  
  
      var Point = function (x, y, time) {
          this.x = x;
          this.y = y;
          this.time = time || new Date().getTime();
      };
  
      Point.prototype.velocityFrom = function (start) {
          return (this.time !== start.time) ? this.distanceTo(start) / (this.time - start.time) : 1;
      };
  
      Point.prototype.distanceTo = function (start) {
          return Math.sqrt(Math.pow(this.x - start.x, 2) + Math.pow(this.y - start.y, 2));
      };
  
      var Bezier = function (startPoint, control1, control2, endPoint) {
          this.startPoint = startPoint;
          this.control1 = control1;
          this.control2 = control2;
          this.endPoint = endPoint;
      };
  
      // Returns approximated length.
      Bezier.prototype.length = function () {
          var steps = 10,
              length = 0,
              i, t, cx, cy, px, py, xdiff, ydiff;
  
          for (i = 0; i <= steps; i++) {
              t = i / steps;
              cx = this._point(t, this.startPoint.x, this.control1.x, this.control2.x, this.endPoint.x);
              cy = this._point(t, this.startPoint.y, this.control1.y, this.control2.y, this.endPoint.y);
              if (i > 0) {
                  xdiff = cx - px;
                  ydiff = cy - py;
                  length += Math.sqrt(xdiff * xdiff + ydiff * ydiff);
              }
              px = cx;
              py = cy;
          }
          return length;
      };
  
      Bezier.prototype._point = function (t, start, c1, c2, end) {
          return          start * (1.0 - t) * (1.0 - t)  * (1.0 - t)
                 + 3.0 *  c1    * (1.0 - t) * (1.0 - t)  * t
                 + 3.0 *  c2    * (1.0 - t) * t          * t
                 +        end   * t         * t          * t;
      };
  
      return SignaturePad;
  })(document);
  
  return SignaturePad;
  
  }));